The first thing you need to confirm before you purchase is compatibility. Not all the units will utilise the data on the cards.

Pop over here to confirm compatibility - https://www.c-map.com/device-search/

Worth noting - the Hook (Reveal) and new Eagle range will not work with the Reveal Relief Shading. The Elite and HDS is required.

Once it's confirmed the card will work in your unit, it is generally a simple case of inserting the Micro SD Card (which is supplied in a larger SD Card Adapter) into your unit. 

Most units will recognise the inserted card and ask if you want to use the data on the card.

If it doesn't, you can manually change it in the system.

Once you have loaded up the charts, you might still not see all the detail you expected. More than likely, you will need to go in and turn on 'high resolution bathermetry' and, if using a Reveal Card, 'Relief Shading'. This should get you all the data off the card showing on your Fishfinder.